Time is fast running out for Syria to hand over its chemical weapons stocks, the international body in charge of their destruction says.

Syria promised to hand over its remaining stocks of chemical weapons ingredients by 27 April.

The UN has set a deadline of 30 June for their full destruction, in a process that should take about 60 days.

Russia brokered a deal between Syria and the UN last year that averted punitive US missile strikes.

A crisis had arisen after the mass gassing of Syrian villagers on 21 August, in which hundreds were killed. Most countries blamed the attack on Syrian government forces but Syria and its allies said rebels were to blame.

Removing Syria's chemical weapons

According to the UN, most of Syria's chemical agents are in a raw or semi-processed state, which should make them easier to dispose of.

The Syrian government is responsible for moving the chemicals from 12 storage sites around the country to the port city of Latakia.

US military container ship the Cape Ray has been fitted out with two $5m (£3m) mobile hydrolysis systems, which break down chemical agents with hot water, then further neutralises them with bleach or sodium hydroxide - also known as caustic soda.

Between them, they can process five to 25 tonnes per day, depending on the material being treated.

The US military has been using the system for a decade on land to dispose of its own chemical weapons, but it is the first time that it has been deployed at sea.

Speaking aboard the M/V Cape Ray, the specially adapted US cargo ship that will neutralise the chemicals at sea, a spokesman for the Organisation for the Prohibition of Chemical Weapons (OPCW) said Syria needed to hand over its remaining stocks within 17 days if it was to avoid being in breach of the deadline.

As of this week, the OPCW said it had only received 54% of Syria's declared 1,200 tons of chemical weapons, and only 43% of "Priority One" materials - those too toxic to be sent to a commercial processing plant.

That means an estimated 552 tons of chemical stocks are still on the ground in Syria, waiting to be transported by armed convoy to the port of Latakia.

The OPCW has two ships, one Danish and one Norwegian, waiting just outside Syrian territorial waters, to go in and take delivery of the remaining chemicals.

Media captionAnna Holligan takes a close-up look at what is on board the Cape Ray

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Hydrolysis units to neutralise the chemical agents, being installed on the US ship MV Cape Ray

Image copyrightCBARRImage caption
Twin hydrolysis systems have been installed on the Cape Ray, to process some 560 tonnes of chemicals

Once they have the full quota, the Norwegian vessel will take its cargo of less toxic chemicals from Latakia directly to commercial disposal facilities in Finland and Texas.

The Danish vessel, the Ark Futura, will sail to the container terminal of Gioia Tauro in southern Italy.

There it will meet the M/V Cape Ray, a specially adapted 35,000-ton US cargo ship, and spend up to 48 hours trans-loading 560 tons of dangerous chemicals, including 21 tons of mustard gas, the only battle-ready chemical weapon in Syria's arsenal. The Danish ship will sail on to Ellesmere port in Britain to deliver 150 tons of less toxic chemicals for disposal.

The M/V Cape Ray will then undertake what has never been done before: neutralising much of an entire country's arsenal of poison gas and its components - at sea. Below deck, the ship is equipped with two units called Field Deployable Hydrolysis Systems (FDHS) - a complex combination of pipes, valves, vats and gauges, monitored by teams of scientists, many of whom will need to wear full biological protective suits during the process.

The time it will take to "neutralise" Syria's chemical stocks depends on how calm the seas are, using hot water and "reagents" to break down the dangerous compounds.

The whole process will be closely monitored by OPCW inspectors who say it will be done safely and in an environmentally secure way. The resulting effluent will then be taken to Bremen in Germany and Kotka in Finland for commercial destruction.

Several Mediterranean countries have expressed concern at the prospect of such dangerous chemicals being transported and processed close to their coasts. But both the US navy's Rear-Admiral Bob Burke and OPCW spokesman Michael Luhan said they did not anticipate any leaks at all.

"Letting chemicals escape from this process," said Mr Luhan, "would be like trying to break out of a maximum security prison."

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Some analysts have suggested destroying chemicals in situ, rather than transport them long distances

1. The Syrian authorities are responsible for packing and safely transporting the chemical weapons from 12 sites across the country to the port of Latakia. Russia has supplied large-capacity and armoured lorries, while the US has sent container drums and GPS locators.

2. Russia is providing security for loading operations at Latakia, for which the US has supplied loading, transportation and decontamination equipment. China has sent 10 ambulances and surveillance cameras, and Finland an emergency response team in case of accidents.

3. Denmark and Norway are providing cargo ships and military escorts to take the chemicals to the container port of Gioia Tauro in Italy. Russia and China are also providing naval escorts. The first consignment of 16 tonnes left Latakia on 7 January.

4. In Italy, the "most critical" chemical agents will be loaded onto the US Maritime Administration cargo ship, MV Cape Ray, to be destroyed by hydrolysis in international waters. Less-toxic chemicals will be shipped by Norwegian and Danish vessels for disposal at commercial facilities.